The present invention disclosed herein relates to an apparatus and method for correcting a three dimensional space-angle of a drill for a dental hand piece.
In general, a dental hand piece is used for cutting or drilling a tooth or an alveolar bone. The dental hand piece is provided at its front end with a rotatable drill.
The demands for accurate dental surgical procedure using the dental hand are increasing. Technology for satisfying demands for a teeth grinding surgical procedure and an implant placement surgical procedure that are two axes of a modern dental surgical procedure has been greatly developed. The accurate dental surgical procedure improves surgical completion, increases a life span of the dental prosthetics, and reduces the time spent for operating the dental surgical procedure. Furthermore, the accurate dental surgical procedure enables a minimally invasive technique that reduces complications after surgery. Particularly, the accuracy of the angle of the dental hand piece is more important for forming an abutment of a metal-ceramic crown and placing the implant.
Sufficient maintenance and proper resistance form for preventing the performance of the metal-ceramic crown from being removed are essential. The maintenance of a cast restoration is determined by a convergence angle of a grinded portion, a surface area, an inner surface roughness of the crown, and the like. Among these, the convergence angle is a primary factor and many researches for the convergence angle have been done. The convergence angle means an angle between extensions of two shaft walls that are formed on the abutment through the grinding of the teeth and faces each other. The convergence angle has an influence on maintenance of restoration. It is known that the optimal convergence angle is between 5 degrees and 12 degrees. In addition, the accuracy of the convergence angle is also important for the best esthetic appreciation for the dental implant placement and the long life span of the implant. The implant placement angle determines the direction of occlusal force applied to the implant and the retention force of the restorations. Especially, when two or more dental implants are placed, the placement angles between different implants critically determine the performance and life span of the implants.
As described above, the accurate angle in the dental surgical procedure is very important. However, the existing dental hand piece cannot satisfy such importance in the dental surgical procedure. This is well shown in the convergence angle research of the abutment for the metal-ceramic crown. Analogy results of the convergence angles of the abutments of 478 metal-ceramic crowns in the practical surgical procedure show that the mean convergence angle is 21 degree and there are big differences in the convergence angles according to dentists. Other researches also report that the convergence angle in the grinding of the abutment is 14-20 degrees. This supports the above facts. These values significantly deviate from the ideal value. The increase of the convergence angle results in the reduction of the mean retention force regardless of the kind of the cement used. The inferiority in fixing-type prosthetics is caused by ceramic fracture (16%) and then by defective adhesiveness (15.1%) due to low retention force. The defective adhesiveness can be prevented by preventing the increase of the convergence angle.
The above-described inaccuracy is resulted from the operator using the existing hand piece who depends on her/his motion skill and space perception ability. Particularly, it is very difficult to reach an optimal three-dimensional angle of the hand piece drill in a three-dimensional space due to physiological limitation of the human. Except for a few master dentists having a unique talent and experiences for many years, most of the dentists have difficulty in reproducing the optimal dental surgical procedure. In order to overcome such limitation and improve overall dental surgical procedure quality, there is a need to objectively measure the dental surgical procedure and develop an auxiliary apparatus showing such objective measurement.
To this end, new methods cooperating with computers have been developed. Particularly, the implant placement surgery has reached the level of a computer guided navigation system that can setup a pre-operation plan through a 3D CT and planning software and can implement the pre-operation plan using surgical guide and optical tracking apparatuses. Furthermore, there is a method using an electromagnetic tracker, and an instrument like a parallel-A-prep that enables direct surveying in the mouth upon tooth grinding is being sold on the market.
In spite of such technical development, many limitations must be overcome in order to utilize the computer guided navigation system in the clinic practice. In order to use the above-described surgical guide or the optical tracking, a bulky and expensive hardware and a complicated process are required. In addition, reference bodies for the surgical guide and the optical tracking can reproduce and must be perfectly fit to patients, it is actually impossible to guarantee in all operation circumstances. Especially, in the surgical guide, a gap between a drill and a hole inevitably exists to supply cooling water to an implant placing portion. Accordingly, there may be an angle error that is greater at an alveolar coronal than at an alveolar apical. In addition, the method using the electromagnetic tracker has a limitation in that the accuracy is relative low and a measured value of metal prosthetics in the mouth may be unstable. When the navigation system is used, the operation time increases and thus the risk also increases because the referencing time in the implant surgical procedure and the navigation time are long. For the parallel-A-Prep that is used for the accurate path of insertion when the tooth is grinded, the volume of the apparatus is too big and the installation is complicated.